Archived posting to the Leica Users Group, 2000/08/05
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Then why wouldn't the two 50mm lenses read the same? The differences in focal lengths cannot explaint that one. I don't think angles of observation matter, since I repeated the test 10 times and always got the same results. Maybe it's omitting 4 air-to-glass surfaces. Miro Jurcevic wrote: > My understanding from what I have been told about lenses, is that the light > geometry of different focal lengths determines the F-stop for that focal > length. > > Essentially, it is possible to have a different exposure for 50mm f2 and > 85mm f2, since the f-stop is a ratio of focal length to lense diameter. The > longer focal length is metering a smaller area of the same space and would > in effect be metering less light per given area. > > Secondly, there is no similarity between the three metering systems and the > bias toward factory settings. Unless we are using a single scientific meter > will all four objectives. > > Thirdly, variations in angle of observation, even angles less than 10 > degrees, can alter the reflected angle entering the metering system. > > These comments are based on the physics of the scene that you have > described. There is simply more than one variable being tested. > > Miro > > > Canon 50/1.5 @f/2 = Between 1/250 and 1/500 sec > > Nikkor 85/2 @ f/2 = 1/250 sec > > M-Hexanon 50/2 @f/2 = 1/250 sec > > M-Hexanon 90/2.8@ f/2.8 = 1/125 sec > > - -- ------------------------------------------------------------------------ Dante Stella http://www-personal.umich.edu/~dante